Busy Web sites are often hosted by a farm of a plurality of servers, each of which handles connections with a portion of the clients. Generally, such a farm includes a load balancer, which receives the packets (referred to also as frames) directed to the Web site of the farm. The load balancer distributes the packets between the plurality of servers, which host the site, such that all the packets of a single client session are transferred to a single server. Server load balancers are also used for other purposes, such as, redirection of packets to proxy caches.
In some cases, the load on the load balancer is very large and an additional and/or a newer load balancer is required. Replacing and/or adding load balancers, however, may require intensive programming such that the new balancer operates according to the operation rules of the old load balancer or that the additional load balancer properly cooperates with the old load balancer.
A load-balancing accelerator solves this problem by learning how to distribute packets directed to the Web site (i.e., having the destination IP address of the Web site) based on the behavior of the old load balancer, referred to herein as the accelerated load balancer. The packets directed from clients to the Web site are routed to the load balancer through the accelerator which listens to the packets and creates entries in an acceleration table for each group of packets. The group of packets are defined based on the five parameters which generally define communication sessions, i.e., the source and destination IP addresses, the protocol and the source and destination ports. In addition, the packets from the load balancer to the servers pass through the accelerator which listens to the packets and searches for matching entries. The accelerator extracts, from packets forwarded by the load balancer which match entries in the table, the destination server of the packets and adds it to the respective entry. Subsequent packets passing through the accelerator, from clients to the load balancer, which match an entry of the table that includes a server identification, are forwarded by the accelerator directly to the server.
Some load balancers, referred to herein as triangulation load balancers, change the destination MAC address and VLAN of the packets they forward, according to the load balancing decisions, but do not change the information in the IP header of the packets. Other load balancers change the destination IP address and/or port of packets which they forward to the servers, in a scheme referred to as half NAT (Network Address Translation) forwarding. These half NAT load balancers must intercept the packets from the servers to the clients in order to change the source address of these packets from the address of the servers to the address of the farm, i.e., the Internet site. Other load balancers change both the source and destination IP addresses of packets which they forward to the servers. These load balancers are referred to as full NAT balancers.
The above described accelerator is suitable for use with triangulation load balancers. These accelerators, however, are not suitable for use with half NAT and full NAT load balancers since the change in the IP address by the load balancer prevents the accelerator from finding entries in the table which match the packets forwarded to the servers.